【JVM】-NO.110.JVM.1 -【hsdis jitwatch 生成查看汇编代码】

Style：Mac

Series：Java

Since：2018-09-10

End：2018-09-10

Total Hours：1

Degree Of Diffculty：5

Degree Of Mastery：5

Practical Level：5

Desired Goal：5

Archieve Goal：3

Gerneral Evaluation：3

Writer:kingdelee

Related Links：

http://www.cnblogs.com/kingdelee/

http://yunjiechao-163-com.iteye.com/blog/2386423

https://blog.csdn.net/unei66/article/details/26477629

https://blog.csdn.net/hengyunabc/article/details/26898657

1.需要下载编译，如果编译失败，可以下载已经编译好的

https://www.chrisnewland.com/updated-instructions-for-building-hsdis-on-osx-417

最终要将 hsdis-amd64.dylib

存放在以下目录：

/Library/Java/JavaVirtualMachines/jdk1.8.0_181.jdk/Contents/Home/jre/lib/server 

public class DynamicDispatch {

//	static abstract class Human {
//		protected abstract void sayHello();
//	}

	static  class Human {
		protected  void sayHello(){
			System.out.println("hello");
		}
	}

	static class Man extends Human {
		@Override
		protected void sayHello() {
			System.out.println("man say hello");
		}
	}

	static class Woman extends Human {
		@Override
		protected void sayHello() {
			System.out.println("woman say hello");
		}
	}

	public static void main(String[] args) {
		Human man = new Man();
		Human woman = new Woman();
		man.sayHello();
		woman.sayHello();
		man = new Woman();
		man.sayHello();
	}
}

　

用如下命令行可以更多地了解内联优化的实际情况以及优化发生的级别：

java -XX:+PrintCompilation -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlining -XX:+TieredCompilation DynamicDispatch

　　

查看JIT生成的汇编代码

-XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly

如果只查看某个方法产生的汇编代码，可以使用命令：

https://zeroturnaround.com/rebellabs/why-it-rocks-to-finally-understand-java-jit-with-jitwatch/　　

　

-XX:+UnlockDiagnosticVMOptions-XX:+PrintAssembly